Where does DNA come from? What is DNA? What is a Down syndrome? DNA comes from our parents, we get half from mom and half from dad. DNA is made up of two strands of nucleotide bases wound into a double helix. The four nucleotide bases are adenine, thymine, cytosine and guanine. Adenine associates with thymine and guanine with cytosine. Each set contains 23 single chromosomes, 22 autosomes and one X or Y sex chromosome (Massimini, 2000). “Your mother can only give you an X chromosome, but your father can give you an X or Y chromosome. If you receive an If you receive a Y chromosome from your father, then your XY pair is genetically male (mayoclinic). Trisomies occur when there is an extra chromosome. An example of this would be that we have a total of 46 chromosomes (23 from each parent). When an extra chromosome is added, it is a trisomy because there are now 47 chromosomes. “There are two different forms of trisomy: partial trisomy – part of a chromosome attaches to another chromosome, and mosaic trisomy – each cell contains an extra one” (Massimini, 2000, p. 48). DNA replication occurs when cells make copies before dividing. DNA is held together by hydrogen bonds. The hydrogen bonds are broken by an enzyme and the DNA polymerase forms a complementary strand to each parent strand. DNA polymerase moves along the DNA strand and uses the bases as a template to create a new DNA strand. It matches A with T and G with C as it moves along the strand. DNA liagase is the glue that seals the spaces that hold the new strand together. The DNA polymerase proof reads its work and corrects any errors it finds. If an error is not corrected, the error will become a mutation, c...... middle of paper ...... getting pregnant. If the other partner is also a carrier, the baby will express the disorder. References Evans-Martin, F. (2009). Down syndrome genes and disease. New York, New York. Chelsea House, Infobase edition Martini, H., Nath, J. and Bartholomew, E., (2012). Fundamentals of Anatomy and Physiology 9th Edition, California, Pearson PublishingMassimini, K. (2000). Genetic Disorders Sourcebook, 2nd Edition, Michigan, OmnigraphicsMayoclinic Staff. (August 17, 2010). Triple Lifespan Development, 13th Edition, New York, New York. McGraw-HillStarr, C., Evers, C., & Starr, L. (2009). The biology of today and tomorrow with physiology. Mason, Ohio. Cengage Learning FoundationTrisomy 18. (2010). Trisomy 18. Retrieved from http://www.Trisomy18.org